The mechanism of hepatic intracellualr heme transport and factors which govern intracellular heme distribution will be examined using isolated hepatocytes, radioisotopic tracers, and protein separation techniques. A dual radioisotope pulse method using 3H, 14C, or 59Fe enriched precursors of heme will be employed to identify potential, cytosolic heme transport proteins. These proteins will be purified and antibodies developed to them. The antibodies will be used to more clearly define the role of these putative heme carriers in the transport and intracellular distribution of heme. In this manner, we may define the nature of the hepatic "free heme pool" which is postulated to contain heme that has not been committed to serve as the prosthetic group for hepatic enzymes such as cytochrome P-450.